1. Field of the Invention
The present invention relates to a control apparatus for an automatic transmission and control method for the automatic transmission, and more particularly relates to the control apparatus for the automatic transmission and the control method therefore capable of performing gear shifting without any gear shift schedule map by calculating a gear shift point.
2. Description of the Related Art
In the past, a gear shift schedule map used in the control apparatus for the automatic transmission is determined at developing stage of a vehicle in taking its fuel consumption characteristic, its acceleration characteristic and the like into consideration, and the gear shift schedule map is stored in a memory element mounted in the vehicle. According to this method, it is possible to control in real time with a computer having a slow calculating speed since data necessary for control can be read out from the gear shift schedule map. However, in recent time, there is a growing need for more comfortable drive and more elaborate transmission control apparatus, which leads to a complex pattern of gear shift schedule.
For example, in a technology described in Japanese Patent Application Laid-Open No. 54-5167 (1979), only break points on a gear shift curve determined by load and engine speed are stored, and break points are read out when they are required to calculate a gear shift schedule by interpolating the break points. In a technology described in Japanese Patent Application Laid-Open No. 55-500122 (1980), a gear shift schedule can be changed corresponding to engine torque. In a technology described in Japanese Patent Application Laid-Open No. 1-238748 (1989), how a driver intends to drive a vehicle is judged according to data such as operating amount of accelerating pedal, operation amount of brake pedal, operating amount of steering wheel, vehicle speed and so on , and condition of road, and then a gear shift schedule fit to the driver is selected. In a technology described in Japanese Patent Application Laid-Open No. 62-246655 (1987), several different kinds of gear shift schedules are set trough calculation depending on driving condition. In these technologies, the gear shift schedule map is stored in its memory element in advance when the vehicle is developed. Since the gear shift schedule map depends on various parameters such as not only fuel consumption characteristic, acceleration characteristic, but also difference in individual driver's habits, difference in driving environments, difference in acceleration characteristics of respective vehicles, difference in engine braking characteristics, it takes a very long time to develop the gear shift schedule map.